Abstract
Working memory ability continues to mature into adulthood in both humans and non-human primates. At the single neuron level, adolescent development is characterized by increased prefrontal firing rate in the delay period, but less is known about how coordinated activity between neurons is altered. Local field potentials (LFP) provide a window into the computation carried out by the local network. To address the effects of adolescent development on LFP activity, three male rhesus monkeys were trained to perform an oculomotor delayed response task. The animals were required to remember a visual stimulus through a 1.5 second delay period and report with a saccade. They were then tested at both the adolescent and adult stage. Simultaneous single-unit spiking (adolescent N = 298, adult 392) and LFP (adolescent N = 130, adult 164) signals were recorded from areas 8a and 46 of the dorsolateral prefrontal cortex (dlPFC). In both the cue and delay period, power relative to baseline decreased in the beta frequency range (16 - 32 Hz) and increased in the gamma frequency range (32 - 128 Hz). However, the adult dlPFC had fewer sites with significant gamma modulation (63% vs. 88%, Fisher’s exact test, p < 0.001). The adult dlPFC also showed weaker stimulus tuning in the low gamma range (32 – 64 Hz) as revealed by the percentage of explained variance. On the other hand, adult dlPFC neurons exhibited sharper delay tuning and elevated firing rate to the best location from 12.0 to 16.5 spikes per second (t-test, p < 0.001), predominantly at sites with significant LFP gamma power modulation and tuning. The results suggest a decrease in inhibitory neuronal interactions after adolescence, in agreement with previous reports for the monkey dlPFC, which leads to a decrease in gamma power and tuning to achieve improved working memory in adulthood.